Bacterial resistance to beta -Iactam antibiotics continues to become more prevalent and more clinically important. A large part of the resistance can be understood and investigated experimentally in terms of the chemistry of the interactions of a -Iactam antibiotics with the active sites of two groups of bacterial enzymes, the beta -Iactamases on one hand, which catalyze the hydrolysis of the antibiotics, and the D-alanyI-D-alanine transpeptidase/carboxypeptidases on the other, which catalyze the synthesis and maintenance of the peptide cross-links of bacterial cell walls, and which are inhibited by beta -Iactam antibiotics. There is now good reason to believe that all of these beta -Iactam binding sites have much in common. An understanding of the structure and function of these sites and of the relationship between them is fundamental to future antibiotics design - both beta -lactam and otherwise. The object of the proposed research is to explore further the chemical functionality and the substrate binding properties of a series of these active sites, using a number of modified substrates, novel inhibitors and potential effectors. Particular focus will be on the development of ligands, substrate and inhibitors, for the transpeptidases which, to date, have exhibited little in vivo activity except with beta -lactams. This goal will be accomplished by a combination of rational design, combinatorial chemistry, and target-accelerated methods. Crystal structures will be used in conjunction with molecular modeling to interpret the results obtained and apply them to further ligand design. These studies will lead to new insight into the chemistry of beta -Iactamase and transpeptidase active sites, and thus to new directions in antibiotic design.